Central decoding controller and controlling method thereof

ABSTRACT

A central decoding controller and a central decoder controlling method are disclosed. A video stream is processed and transmitted via at least two parallel channels. The method comprises steps of: receiving a video key frame obtained by decoding an original video frame via a first channel, and a plurality of intra-description frames neighboring the video key frame; receiving a predictive video frame obtained by processing a prediction analysis and an error correction to the original video frame via a second channel parallel to the first channel; receiving a plurality of inter-description frames via the second channel, the inter-description frames neighboring the video key frame; calculating correlation of the video key frame, the intra-description frames, and the inter-description frames; and selecting the video key frame or the predictive video frame as an output frame according to the correlation result. The method can improve video quality under wireless transmission or unstable internet transmission.

This invention is partly disclosed in an published dissertation ofNational Taiwan University of Science and Technology, entitled “ANIMPROVED CENTRAL DECODER FOR MULTIPLE DESCRIPTION CODER INTEGRATED WITHDISTRIBUTED VIDEO CODER,” completed by Jyun-Jie Jhuang, and published onJul. 24, 2009.

CLAIM OF PRIORITY

This application claims priority to Taiwanese Patent ApplicationPublication No. 099101789 filed on Jan. 22, 2010.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a central decoding controller and acontrolling method thereof, and more particularly, to a central decodingcontroller and a controlling method adopting correlation operations.

BACKGROUND OF THE INVENTION

Multiple Description Coding (MDC) is an effective solution ofmulti-media transmission in the jammed internet and unstable wirelessnetworks. The MDC promises the stability and reliability of multi-mediacommunications with multiple transmission paths. Distributed VideoCoding (DVC) redistributes the coding complexity from an encoder to adecoder for the sake of providing video communications for mobiledevices (e.g. cell phones, PDAs).

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a central decodingcontroller and controlling method thereof, for dynamically selecting avideo frame of higher quality as an output frame.

Another objective of the present invention is to provide a centraldecoding controller and controlling method thereof, for improving videoquality under wireless transmission or unstable internet transmission.

According to the above objectives, the present invention provides acentral decoder controlling method, in which a video stream is processedand transmitted via at least two parallel channels, the method comprisessteps of: receiving a video key frame obtained by decoding an originalvideo frame via a first channel, and a plurality of intra-descriptionframes neighboring the video key frame; receiving a predictive videoframe obtained by processing a prediction analysis and an errorcorrection to the original video frame via a second channel parallel tothe first channel; receiving a plurality of inter-description frames viathe second channel, the inter-description frames neighboring the videokey frame; calculating correlation of the video key frame, theintra-description frames, and the inter-description frames; andselecting the video key frame or the predictive video frame as an outputframe according to the correlation result.

The present invention further provides a central decoding controller, inwhich a video stream is processed and transmitted via at least twoparallel channels, the central decoding controller comprises: a firstterminal for receiving a video key frame obtained by decoding anoriginal video frame via a first channel, and a plurality ofintra-description frames neighboring the video key frame; a secondterminal for receiving a predictive video frame obtained by processingan a prediction analysis and an error correction to the original videoframe via a second channel parallel to the first channel, and aplurality of inter-description frames via the second channel, theinter-description frames neighboring the video key frame; a correlator,coupled to the first terminal and the second terminal, for calculatingcorrelation of the video key frame, the intra-description frames, andthe inter-description frames; an estimating logic and controller,coupled to the correlator, for controlling the correlator and outputtinga signal according to the correlation result; and a multiplexer,receiving the video key frame from the first terminal and the predictivevideo frame from the second terminal, the multiplexer being coupled tothe estimating logic and controller, in which the estimating logic andcontroller controls the multiplexer to select the video key frame or thepredictive video frame as an output frame.

In the present invention, the two video codec approaches, MDC (multipledescription codec) and DVC (distributed video codec), abbreviated asMDVC, can be effectively integrated to provide stable transmission andhigh efficient video coding. The MDVC would yield two separate videodescriptions, and each comprises one key frame bit-stream and oneWyner-Ziv (WZ) frame bit-stream.

In the present invention, a predictive coding is adopted in the MDVC.The predictive coding can reduce the signal entropy in an encoding sideand thus improve video quality in a decoding side.

In the present invention, the error correlation among intra-descriptionsand inter-descriptions are utilized in the central decoding controllerof the MDVC to dynamically select the best reconstructed frames from thetwo descriptions, instead of selecting only one description or selectingonly key frames from the two descriptions, to yield the reconstructedvideo.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in details in conjunction withthe appending drawings.

FIG. 1 is a structure diagram showing a video delivery systemimplemented according to the present invention.

FIG. 2 is a structure diagram showing an encoder of the video deliverysystem shown in FIG. 1.

FIG. 3 is a structure diagram showing a decoder of the video deliverysystem shown in FIG. 1.

FIG. 4 is an exemplary diagram showing Wyner-Ziv codec.

FIG. 5 is an exemplary diagram showing the central decoder controllingmethod of the present invention.

FIG. 6 is a flow chart showing the central decoder controlling method ofthe present invention.

FIG. 7 is a structural diagram showing the central decoding controllerof the present invention.

FIG. 8 is an exemplary diagram showing correlation operation of thecentral decoder controlling method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, it is a structure diagram showing a video deliverysystem 1 implemented according to the present invention. The videodelivery system 1 is a system combining a multiple description codec(MDC) with a distributed video codec (DVC), abbreviated as MDVC, whichis capable of providing reliable and stable video transmission underwireless networks or jammed, unstable internet transmission.

As shown in FIG. 1, the video delivery system 1 includes an encoder 31and a decoder 32. The encoder 31 has a de-multiplexer 5, a first sideencoder (E1) 11, and a second side encoder (E2) 21. The decoder 32 has afirst side decoder (D1) 12, a second side decoder (D2) 22, and a centraldecoding controller (Dc) 40.

An original video input is separated into video streams by thede-multiplexer 5 in the beginning, and then the video streams aretransmitted and proceeded via a plurality of channels such as a firstchannel 10 and a second channel 20 in the video delivery system 1. Onevideo stream is encoded by the first side encoder (E1) 11 and decoded bythe first side decoder (D1) 12 via the first channel 10. The other videostream is encoded by the second side encoder (E2) 21 and decoded by thesecond side decoder (D2) 22 via the second channel 20. The two decodedvideo streams are transmitted to the central decoding controller (Dc)40. The central decoding controller will select to output the videoframes which are better in quality.

Referring to FIG. 2, it is a structure diagram showing the encoder 31 ofthe video delivery system 1 shown in FIG. 1. In the encoder 31, eachside encoder (E1, E2) 11, 21 comprises a scalable video encoder 52, andan ECC (error correcting codes) encoder 58. The scalable video encoder52 can be implemented as an MC-EZBC encoder. The ECC encoder 58 can beimplemented as a Wyner-Ziv encoder. In addition, each side encoder (E1,E2) 11, 21 has an encoding mode selector 55. The video delivery system 1can be operated in three modes, i.e. mode 0, mode 1, and mode 2. Themode 0 denotes pulse-code modulation (PCM) and is abbreviated asMDVC-DCT. The mode 1 denotes that differential pulse-code modulation(DPCM) is used, and is abbreviated as MDVC-RDCT1. In addition, the mode2 denotes simplified DPCM and is abbreviated as MDVC-RDCT2. In the videodelivery system 1, similar or the same operations are proceeded in thefirst side encoder (E1) 11 and the second side encoder (E2) 21 forrespectively outputting information D1 and D2. Therefore, the detaileddescription about the second side encoder (E2) 21 is omitted herein.

In the encoder 11, the original video input is separated into videoframes of odd and even subsequences, i.e. I_(2i) and I_(2i+1), by thede-multiplexer 5. The odd subsequences and the even subsequences aretransmitted respectively via the scalable video encoders 52 of the firstside encoder (E1) 11 and the second side encoder (E2) 21 for providingkey frames, denoted as So and Se respectively. On the other hand, theeven subsequence (I_(2i)) is also transmitted to the first side encoder(E1) 11. The even subsequence (I_(2i)) and a predictive image (Ĩ_(2i)^(P(E))) are utilized to yield a residual signal (r_(2i) ^(E)), and theresidual signal (r_(2i) ^(E)) is utilized for encoding into a WZ frame(r_(e)). Similarly, the odd subsequence (I_(2i−1)) is also transmittedto the second side encoder (E2) 21 for obtaining a WZ frame (r_(o)). Theresidual signal (r_(2i) ^(E)) is a prediction error to the I_(2i) image,and is substantially equal to the difference between the I_(2i) imageand the predictive image (Ĩ_(2i) ^(P(E))). The predictive image (Ĩ_(2i)^(P(E))) is predicted from a reconstructed image (Ĩ_(2i−1) ^(E)) whichis decoded from a scalable video decoder 53, and the predictive image(Ĩ_(2i) ^(P(E))) is selected from a predictive image selector 54. Duringprocessing the residual signal (r_(2i) ^(E)) in the Wyner-Ziv encoder, atransformer 56 operates discrete cosine transform (DCT) to generatecoefficient bands, a quantizer 57 performs quantization operation to thecoefficient bands, and an ECC encoder 58 executes error correction so asto generate the WZ frame (r_(e)). By the above-mentioned operations, theD1 information generated from the first side encoder (E1) 11 on thefirst channel 10 includes key frames (So) and their residualinformation, i.e. the WZ frames (r_(e)), and the D2 informationgenerated from the second side encoder (E2) 21 on the second channel 20includes key frames (Se) and their residual information, i.e. the WZframes (r_(o)).

Referring to FIG. 3, it is a structure diagram showing the decoder 32 ofthe video delivery system 1 shown in FIG. 1. The decoder 32 includes thefirst side decoder (D1) 12, the second side decoder (D2) 22, and thecentral decoding controller (Dc) 40. In the decoder 32, each sidedecoder (D1, D2) 12, 22 comprises a scalable video decoder 62, and anECC (error correcting codes) decoder 68. The scalable video decoder 62can be implemented as MC-EZBC decoder. The ECC decoder 68 can beimplemented as Wyner-Ziv decoder. The D1 information is inputted to thefirst side decoder (D1) 12. The key frames (So) are decoded andreconstructed into an image (Ĩ_(2i−1) ^(D)), and then outputted to thecentral decoding controller (Dc) 40. The key frames (So) are alsoutilized to provide side information (SI) for the ECC decoder 68. Thekey frames (So) and their residual information, i.e. the WZ frames(r_(e)), are utilized to be reconstructed into video frames of evensequence (Ĩ_(2i) ^(WZ)) by the ECC decoder 68. The second side decoder(D2) 22 performs similar operations to process the D2 information. Thedetailed description to this part is omitted herein. The reconstructedeven sequence (Ĩ_(2i) ^(WZ)) and odd sequence (Ĩ_(2i−1) ^(D)) generatedby the first side decoder (D1) 12 on the first channel 10 and thereconstructed odd sequence (Ĩ_(2i−1) ^(WZ)) and even sequence (Ĩ_(2i)^(D)) generated by the second side decoder (D2) 22 on the second channel20 are transmitted to the central decoding controller (Dc) 40 to beselected to output.

When the reconstructed frames are not much different to the originalvideo frames, i.e. Ĩ_(2i) ^(D) substantially equal to I_(2i), Ĩ_(2i−1)^(D) substantially equal to I_(2i−1), the WZ frames will be abandoned.This is because the central decoding controller (Dc) 40 only needs toselect Ĩ_(2i) ^(D) or Ĩ_(2i−1) ^(D) to yield the best image quality.However, when only one description (such as information D1) is received,the central decoding controller (Dc) 40 still can maintain the videostream stable by using the frames Ĩ_(2i) ^(WZ) although the imagequality is not great as desired.

Decoding mode selectors 65, 65′ respectively in side decoders (D1, D2)12, 22 have similar function as the encoding mode selectors 55 of eachside encoder (E1, E2) 11, 21. The decoding mode selectors 65, 65′ areoperated in three modes, i.e. mode 0, mode 1, and mode 2, for modulatingor decoding video signals. In addition, interpolators 63 are utilizedfor interpolation operations. The functions of predictive imageselectors 64, transformers 66, and quantizers 67 in each side decoder(D1, D2) 12, 22 are similar or the same as the predictive imageselectors 54, transformers 56, and quantizers 57 of each side encoder(E1, E2) 11, 21, respectively. The description is omitted herein.

Referring to FIG. 4, it is an exemplary diagram showing Wyner-Ziv codec.The residual signal (r_(2i) ^(E)) to be encoded by the Wyner-Ziv encoderis the prediction error between the input video frame (I_(2i)) and thepredictive frame (Ĩ_(2i) ^(P(E))). The residual signal (r_(2i) ^(E)) istransformed by the transformer 56 so that related coefficients areobtained. The quantizer 57 performs a quantization operation to thecoefficients to obtain a DCT block. The quantized DCT block isdecomposed into bit-planes by a turbo encoder 71. For each bit-plane,only the parity check bits are transmitted to a turbo decoder 73. Theturbo decoder 73 would request more parity bits if it cannot recover thedata correctly. In addition, a buffer 72 can store the parity checkbits. The above-mentioned operations are implemented as Slepian-Wolfcodec. During reconstructing frames, the side information at the decoderside is obtained by interpolation, bi-directional motion estimation, andthe residual signal estimated according to the frames from the scalablevideo decoder 62.

The predictive image selectors 54, 64 in the encoder 31 and the decoder32 will exploit temporal correlation between adjacent images to reducethe signal entropy of different images. For one image (I_(2i)) to beencoded, it has to find the best predictive one (Ĩ_(2i) ^(P(E))) thatwould yield best rate-distortion efficiency. The predictive image(Ĩ_(2i) ^(P(E))) has less difference to the original one (I_(2i)). Thepredictive image (Ĩ_(2i) ^(P(E))) is selected from the reconstructedimages of the scalable video encoder and decoder 52, 53 in that both theencoder and decoder 52, 53 have to refer to the same image. The bestpredictive image (Ĩ_(2i) ^(P(E))) is selected from three reconstructedimages Ĩ_(2i−1) ^(E), Ĩ_(2i+1) ^(E), and the average of both images. Forthe predictive image selector 54, the procedure to select the bestpredictive image (Ĩ_(2i) ^(P(E))) is described below.

In the beginning, calculate the difference between the original imageframe (I_(2i)) and the average of both the two reconstructed images,Ĩ_(2i−1) ^(E), Ĩ_(2i+1) ^(E), the difference between I_(2i) and Ĩ_(2i−1)^(E), and the difference between I_(2i) and Ĩ_(2i+1) ^(E), representedas ΔI₀=|I_(2i)−P₀(I_(2i))|, ΔI₁=|I_(2i)−P₁(I_(2i))|, andΔI₂=|I_(2i)−P₂(I_(2i))|, respectively. The predictive modes P₀, P₁, andP₂ are

$\frac{{\overset{\sim}{I}}_{{2\; i} - 1}^{E} + {\overset{\sim}{I}}_{{2\; i} + 1}^{E}}{2},$

Ĩ_(2i−1) ^(E), and Ĩ_(2i+1) ^(E), respectively.

When the difference between the original image frame (I_(2i)) andĨ_(2i−1) ^(E), and the difference between I_(2i) and Ĩ_(2i+1) ^(E), areboth smaller than or equal to predetermined thresholds, i.e. ΔI₁≦ε₁ andΔI₂≦ε₂, select the prediction mode P_(i) that minimizes the differences,i.e. ΔI_(i)=min {ΔI₁, ΔI₂}.

When the difference between the original image frame (I_(2i)) andĨ_(2i−1) ^(E), and the difference between I_(2i) and Ĩ_(2i+1) ^(E), areboth greater than the predetermined thresholds, i.e. ΔI₁>ε₁ and ΔI₂>ε₂and |ΔI₁−ΔI₂|≦ε₀, select the prediction mode P₀.

When the difference between the original image frame (I_(2i)) andĨ_(2i−1) ^(E), and the difference between I_(2i) and Ĩ_(2i+1) ^(E), areboth greater than the predetermined thresholds, i.e. ΔI₁>ε₁ and ΔI₂>ε₂and |ΔI₁−ΔI₂|>ε₀, select the prediction mode P_(i) that minimizes thedifferences, i.e. ΔI_(i)=min {ΔI₁, ΔI₂}.

Instead of just selecting the prediction mode P_(i) that yieldΔI_(i)=min {ΔI₁, ΔI₂}, the above-mentioned selection is carried out fromthe viewpoint of video temporal correlation. The distortion ΔI_(i) isproportional to video complexity at that period. When ΔI₁≦ε₁ and ΔI₂≦ε₂,the video should be stable during that interval, and the prediction modeP₁ or P₂ is adopted since the correlation between consequential imagesis high. When both ΔI₁ and ΔI₂ are greater than the thresholds, and|ΔI₁−ΔI₂| is small, the video should be in a high-motion period and thusthe image variation is great. However, the correlations are still equalto each other. When |ΔI₁−ΔI₂| is great, the correlation among thesethree images is small, and thus the prediction mode P₁ or P₂ is selectedto yield the minimum ΔI_(i).

Referring to FIG. 5, it is an exemplary diagram showing the centraldecoder controlling method of the present invention. According to thedescription above, the D1 information in the first channel 10 includeskey frame (So) and error correction codes (i.e. the residual signal orthe WZ frame (r_(e))) of the frame adjacent to the key frame (So). TheD2 information in the second channel 20 includes next or previous keyframe (Se) and error correction codes (i.e. the residual signal or theWZ frame (r_(o))) of the frame adjacent to the key frame (Se).Correspondingly, the first side decoder (D1) 12 on the first channel 10generates the reconstructed frames of odd sequence (Ĩ_(2i−1) ^(D)), andthe frames of even sequence (Ĩ_(2i) ^(WZ)) that have been errorcorrected. The second side decoder (D2) 22 on the second channel 20generates the reconstructed frames of even sequence (Ĩ_(2i) ^(D)), andthe frames of odd sequence (Ĩ_(2i−1) ^(WZ)) that have been errorcorrected. The central decoding controller (Dc) 40 receives thereconstructed frames of even sequence (Ĩ_(2i) ^(D)) and odd sequence(Ĩ_(2i−1) ^(D)), the even sequence (Ĩ_(2i) ^(WZ)), and the odd sequence(Ĩ_(2i−1) ^(WZ)), and then performs a correlation operation to theseframes. The central decoding controller (Dc) 40 will select one of theseframes as an output, according to the result of correlation.

When one description (e.g. the D2 information) can not be receivedcorrectly, the first side decoder (D1) 12 is still able to provide thereconstructed frames of odd sequence (Ĩ_(2i−1) ^(D)) and the frames ofeven sequence (Ĩ_(2i) ^(WZ)) to be outputted. Under this situation, thePSNR would be fluctuated and unpleasant visual quality would bepresented. At different time duration, the D1 information and/or the D2information may subject to transmission errors. These descriptions willbe attacked by noise signals, and the noise will prevent the centraldecoding controller (Dc) 40 from reconstructing video with high quality.However, in the present invention, the central decoding controller (Dc)40 can dynamically select an image I_(i), either from Ĩ_(i) ^(WZ) orĨ_(i) ^(D) image, with high reconstructed quality, as the output video.Therefore, the present invention can improve the quality of videotransmitted under wireless networks or jammed, unstable internettransmission.

Please refer to FIG. 6, FIG. 7, and FIG. 8. FIG. 6 is a flow chartshowing the central decoder controlling method of the present invention.FIG. 7 is a structural diagram showing the central decoding controller40 of the present invention. FIG. 8 is an exemplary diagram showing thecorrelation operation of the central decoder controlling method of thepresent invention. As shown in FIG. 7, the central decoding controller40 of the present invention has a first terminal 41 and a secondterminal 42. The two terminals 41, 42 receive video frames respectivelyfrom the first channel 10 and the second channel 20. The centraldecoding controller 40 comprises a correlator 44, an estimating logicand controller 46, and a multiplexer 48. The correlator 44 is coupled tothe first terminal 41 and the second terminal 42. The correlator 44performs correlation operations to the video frames from the twoterminals 41, 42. The estimating logic and controller 46 is coupled tothe correlator 44, and is utilized for controlling the correlator 44 andoutputting a signal according to the result of correlation. Themultiplexer 48 is controlled by the estimating logic and controller 46,and is utilized for selecting the video frames of best quality as outputframes. The video frames (Ĩ_(2i−1) ^(D), Ĩ_(2i) ^(WZ)) from the firstchannel 10 and the video frames (Ĩ_(2i) ^(D), Ĩ_(2i−1) ^(WZ)) from thesecond channel 20 are received by the multiplexer 48.

Referring to the flow chart shown in FIG. 6, the central decodercontrolling of the present invention will be described in conjunctionwith the central decoding controller 40 shown in FIG. 7 and thecorrelation operation shown in FIG. 8.

In step S10, the second terminal 42 of the central decoding controller40 receives a video key frame reconstructed from the second side decoder(D2) 22 and a plurality of intra-description frames (Ĩ_(2i−2) ^(D),Ĩ_(2i+2) ^(D)) neighboring the video key frame, via the second channel20. The video key frame (Ĩ_(2i) ^(D)) is resulted by decoding andreconstructing an original video frame (I_(2i)) via the second channel20.

In addition, the first terminal 41 of the central decoding controller 40receives a predictive video frame (Ĩ_(2i) ^(WZ)), which is obtained byprocessing a prediction analysis and an error correction to the originalvideo frame (I_(2i)), via the first channel 10 parallel to the secondchannel 20. The predictive video frame (Ĩ_(2i) ^(WZ)) is an imageobtained by predicting the video key frame (Ĩ_(2i) ^(D)).

The first terminal 41 of the central decoding controller 40 receives aplurality of inter-description frames (Ĩ_(2i−1) ^(D), Ĩ_(2i+1) ^(D)) viathe first terminal 10. The inter-description frames are odd framesneighboring the video key frame (I_(2i) ^(D)). The inter-descriptionframes (Ĩ_(2i−1) ^(D), Ĩ_(2i+1) ^(D)) is resulted by decoding andreconstructing odd video frames (I_(2i−1), I_(2i+1)) via the firstchannel 10.

In step S12, the correlator 44 of the central decoding controller 40receives the video key frame (Ĩ_(2i) ^(D)), the intra-description frames(Ĩ_(2i−2) ^(D), Ĩ_(2i+2) ^(D)), and the inter-description frames(Ĩ_(2i−1) ^(D), Ĩ_(2i+1) ^(D)), and performs correlation operations tothese frames. For example, calculate the inter-description frame(Ĩ_(2i−1) ^(D), Ĩ_(2i+1) ^(D)) difference, Δ¹=|Ĩ_(2i+1) ^(D)−Ĩ_(2i−1)^(D)|₂; the difference between the video key frame (Ĩ_(2i) ^(D)) and theintra-description frames (Ĩ_(2i−2) ^(D), Ĩ_(2i+2) ^(D)), Δ⁻ ²=|Ĩ_(2i)^(D)−Ĩ_(2i−2) ^(D)|₂, Δ₊ ²=|Ĩ_(2i) ^(D)−Ĩ_(2i+2) ^(D)|₂; and thedifference between the video key frame (Ĩ_(2i) ^(D)) and theinter-description frames (Ĩ_(2i−1) ^(D), Ĩ_(2i+1) ^(D)), Δ⁻ ¹²=|Ĩ_(2i)^(D)−Ĩ_(2i−1) ^(D)|₂, Δ₊ ¹²=|Ĩ_(2i) ^(D)−Ĩ_(2i+1) ^(D)|₂.

In step S14 and step S16 the estimating logic and controller 46 receivesthe result of the above-mentioned correlation from the correlator 44,and determines or controls according to the result of correlation.

In step S14, the estimating logic and controller 46 determines whetherthe correlation of the video key frame (Ĩ_(2i) ^(D)) and theinter-description frames (Ĩ_(2i−1) ^(D), Ĩ_(2i+1) ^(D)) is greater thanthe correlation of the video key frame (Ĩ_(2i) ^(D)) and theintra-description frames (Ĩ_(2i−2) ^(D), Ĩ_(2i+2) ^(D)), for example,whether the sum of the differences between the video key frame and theinter-description frames is smaller than the sum of the differencesbetween the video key frame and the intra-description frames, i.e. (Δ⁻¹²+Δ₊ ¹²)<(Δ⁻ ²+Δ₊ ²). If yes, the estimating logic and controller 46controls the multiplexer 48 to select the video key frame (Ĩ_(2i) ^(D))as output frame (step S20).

In step S16, when the result determined in step S14 is negative, theestimating logic and controller 46 will determine whether thecorrelation of the video key frame (Ĩ_(2i) ^(D)) and theintra-description frames (Ĩ_(2i−2) ^(D), Ĩ_(2i+2) ^(D)) is greater thantwo times the correlation of the inter-description frames (Ĩ_(2i−1)^(D), Ĩ_(2i+1) ^(D)), for example, whether the sum of the differencesbetween the video key frame and the intra-description frames is smallerthan two times the difference between the inter-description frames, i.e.(Δ⁻ ²+Δ₊ ²)<2·Δ¹. If yes, the estimating logic and controller 46controls the multiplexer 48 to select the video key frame (Ĩ_(2i) ^(D))as output frame (step S20). If no, the estimating logic and controller46 controls the multiplexer 48 to select the predictive video frame(Ĩ_(2i) ^(WZ)) as output frame (step S21). This embodiment takes theeven frames (Ĩ_(2i) ^(D)) as the video key frame. If the video key frameis odd one (Ĩ_(2i−1) ^(D)), the operation is similar or the same. Thedescription is omitted herein.

In addition, according to the above-mentioned determination, theestimating logic and controller 46 outputs an index (0 or 1) as acontrol signal for controlling the multiplexer 48. For example, when theestimating logic and controller 46 outputs the index 1, the multiplexer48 selects the video key frame (Ĩ_(2i) ^(D)) as output frame. When theestimating logic and controller 46 outputs the index 0, the multiplexer48 selects the predictive video frame (Ĩ_(2i) ^(WZ)) as output frame.

The strategy to select the video key frame (Ĩ_(2i) ^(D)) or thepredictive video frame (Ĩ_(2i) ^(WZ)) is described below. (1) The resultdetermined in step S14 is positive. That is, the sum of the differencesbetween the video key frame and the inter-description frames is smallerthan the sum of the differences between the video key frame and theintra-description frames, i.e. (Δ⁻ ¹²+Δ₊ ¹²)<(Δ⁻ ²+Δ₊ ²). It can bereferred that the video key frame (Ĩ_(2i) ^(D)) is not degraded by noiseattack and its quality should be better than the predictive video frame(Ĩ_(2i) ^(WZ)). Hence, the estimating logic and controller 40 selectsthe video key frame (Ĩ_(2i) ^(D)) as output frame. (2) The resultdetermined in step S14 is negative. That is, the sum of the differencesbetween the video key frame and the inter-description frames is muchgreater. It is noted that there are degraded images among these threekey frames, i.e. Ĩ_(2i) ^(D), Ĩ_(2i−1) ^(D), and Ĩ_(2i+1) ^(D). Thecondition (Δ⁻ ²+Δ₊ ²)<2·Δ¹ is then used to make clear which one isdegraded. When this condition is satisfied, the degraded image should beĨ_(2i−1) ^(D) or Ĩ_(2i+1) ^(D), and the predictive video frame (Ĩ_(2i)^(WZ)) would be affected by this degradation. Hence, the estimatinglogic and controller 40 selects the video key frame (Ĩ_(2i) ^(D)) asoutput frame. (3) When both the above-mentioned first and secondconditions failed, it can be referred that the video key frame (Ĩ_(2i)^(D)) is degraded. Hence, the estimating logic and controller 40 selectsthe predictive video frame (Ĩ_(2i) ^(WZ)) as output frame.

While the preferred embodiments of the present invention have beenillustrated and described in detail, various modifications andalterations can be made by persons skilled in this art. The embodimentof the present invention is therefore described in an illustrative butnot restrictive sense. It is intended that the present invention shouldnot be limited to the particular forms as illustrated, and that allmodifications and alterations which maintain the spirit and realm of thepresent invention are within the scope as defined in the appendedclaims.

1. A central decoder controlling method, in which a video stream isprocessed and transmitted via at least two parallel channels, the methodcomprises steps of: receiving a video key frame obtained by decoding anoriginal video frame via a first channel, and a plurality ofintra-description frames neighboring the video key frame; receiving apredictive video frame obtained by processing a prediction analysis andan error correction to the original video frame via a second channelparallel to the first channel; receiving a plurality ofinter-description frames via the second channel, the inter-descriptionframes neighboring the video key frame; calculating correlation of thevideo key frame, the intra-description frames, and the inter-descriptionframes; and selecting the video key frame or the predictive video frameas an output frame according to the correlation result.
 2. The centraldecoder controlling method of claim 1, wherein in the selecting step,when the correlation of the video key frame and the inter-descriptionframes is greater than the correlation of the video key frame and theintra-description frames, select the video key frame as the outputframe.
 3. The central decoder controlling method of claim 2, whereinwhen the sum of the differences between the video key frame and theinter-description frames is smaller than the sum of the differencesbetween the video key frame and the intra-description frames, select thevideo key frame as the output frame.
 4. The central decoder controllingmethod of claim 1, wherein in the selecting step, when the correlationof the video key frame and the intra-description frames is greater thantwo times the correlation of the inter-description frames, select thevideo key frame as the output frame.
 5. The central decoder controllingmethod of claim 4, wherein when the sum of the differences between thevideo key frame and the intra-description frames is smaller than twotimes the difference between the inter-description frames, select thevideo key frame as the output frame.
 6. The central decoder controllingmethod of claim 1, wherein in the selecting step, when the correlationof the video key frame and the inter-description frames is smaller thanthe correlation of the video key frame and the intra-description frames,and the correlation of the video key frame and the intra-descriptionframes is smaller than two times the correlation of theinter-description frames, select the predictive video frame as theoutput frame.
 7. The central decoder controlling method of claim 6,wherein when the sum of the differences between the video key frame andthe inter-description frames is greater than the sum of the differencesbetween the video key frame and the intra-description frames, and thesum of the differences between the video key frame and theintra-description frames is greater than two times the differencebetween the inter-description frames, select the predictive video frameas the output frame.
 8. The central decoder controlling method of claim1, wherein the correlation operation is to calculate the imagedifference between the video key frame, the intra-description frames,and the inter-description frames.
 9. The central decoder controllingmethod of claim 1, wherein the predictive video frame is obtained byutilizing Wyner-Ziv codec.
 10. A central decoding controller, in which avideo stream is processed and transmitted via at least two parallelchannels, the central decoding controller comprises: a first terminalfor receiving a video key frame obtained by decoding an original videoframe via a first channel, and a plurality of intra-description framesneighboring the video key frame; a second terminal for receiving apredictive video frame obtained by processing a prediction analysis andan error correction to the original video frame via a second channelparallel to the first channel, and a plurality of inter-descriptionframes via the second channel, the inter-description frames neighboringthe video key frame; a correlator, coupled to the first terminal and thesecond terminal, for calculating correlation of the video key frame, theintra-description frames, and the inter-description frames; anestimating logic and controller, coupled to the correlator, forcontrolling the correlator and outputting a signal according to thecorrelation result; and a multiplexer, for receiving the video key framefrom the first terminal and the predictive video frame from the secondterminal, the multiplexer coupled to the estimating logic andcontroller, in which the estimating logic and controller controls themultiplexer to select the video key frame or the predictive video frameas an output frame.
 11. The central decoding controller of claim 10,wherein when the estimating logic and controller determines that thecorrelation of the video key frame and the inter-description frames isgreater than the correlation of the video key frame and theintra-description frames, the estimating logic and controller controlsthe multiplexer to select the video key frame as the output frame. 12.The central decoding controller of claim 11, wherein when the estimatinglogic and controller determines that the sum of the differences betweenthe video key frame and the inter-description frames is smaller than thesum of the differences between the video key frame and theintra-description frames, the estimating logic and controller controlsthe multiplexer to select the video key frame as the output frame. 13.The central decoding controller of claim 10, wherein when the estimatinglogic and controller determines that the correlation of the video keyframe and the intra-description frames is greater than two times thecorrelation of the inter-description frames, the estimating logic andcontroller controls the multiplexer to select the video key frame as theoutput frame.
 14. The central decoding controller of claim 13, whereinwhen the estimating logic and controller determines that the sum of thedifferences between the video key frame and the intra-description framesis smaller than two times the difference between the inter-descriptionframes, the estimating logic and controller controls the multiplexer toselect the video key frame as the output frame.
 15. The central decodingcontroller of claim 10, wherein when the estimating logic and controllerdetermines that the correlation of the video key frame and theinter-description frames is smaller than the correlation of the videokey frame and the intra-description frames, and the correlation of thevideo key frame and the intra-description frames is smaller than twotimes the correlation of the inter-description frames, the estimatinglogic and controller controls the multiplexer to select the predictivevideo frame as the output frame.
 16. The central decoding controller ofclaim 15, wherein when the estimating logic and controller determinesthat the sum of the differences between the video key frame and theinter-description frames is greater than the sum of the differencesbetween the video key frame and the intra-description frames, and thesum of the differences between the video key frame and theintra-description frames is greater than two times the differencebetween the inter-description frames, the estimating logic andcontroller controls the multiplexer to select the predictive video frameas the output frame.
 17. The central decoding controller of claim 10,wherein the correlation operation is to calculate the image differencebetween the video key frame, the intra-description frames, and theinter-description frames.
 18. The central decoding controller of claim10, wherein the predictive video frame is obtained by utilizingWyner-Ziv codec.